To reduce costs, the image forming apparatus may be configured such that the plurality of charging members are connected in parallel to a single common power source.
In such a configuration, adhesion of silica to one charging member causes the charging member to possess a higher resistance which in turn causes an amount of an electric current allowed to pass through the charging member to decrease, and would at worst, make the charging member unable to properly charge the corresponding photoconductor drum. To avoid this risk, the total amount of electric current obtained by summing up the amounts of electric current flowing through all the charging members may be monitored for use in regulation of a voltage applied to the charging members so that the total amount of electric current is maintained at a predetermined value. This method is considered to suppress poor charging performance.
Excessive adhesion of silica to one charging member which raises the resistance of that charging member would result in excessive increase in the amount of electric current passing through the other charging member(s), as the case may be. Therefore, a user may have to be notified of the necessity of cleaning the relevant charging member(s) not later than the amount of electric current passing through that charging member(s) reaches an upper limit thereof.
However, the aforementioned total current amount monitoring scheme typically does not provide a user with information as to which charging member is in need of cleaning, and the user would possibly choose to clean only one charging member and forget cleaning other charging member(s) in need of cleaning. If the charging member which the user has forgotten and failed to clean is the most seriously contaminated one (i.e., with more silica adhered), the next printing operation would soon be aborted by an error because the amount of electric current would reach its upper limit.